Automated intraocular lens injector device

ABSTRACT

An intraocular lens injection device comprises a tubular housing with a plunger longitudinally disposed within the tubular housing. An electric drive system longitudinally translates the plunger so that its tip engages an insertion cartridge to fold and displace an intraocular lens disposed within and to inject the folded lens into the lens capsule of an eye. A control circuit is configured to start translation of the plunger, responsive to user input, to detect at least one fault condition based on a counter-electromotive force produced by the electric motor, and to stop translation of the plunger assembly responsive to the detected fault condition, which may comprise excessive resistance to forward or rearward translation of the plunger or insufficient resistance to forward translation of the plunger.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of prior application Ser.No. 12/249,996, filed Oct. 13, 2008, now U.S. Pat. No. 8,308,736, theentire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to a device for delivering anintraocular lens into an eye and more particularly to fault detection insuch a device.

BACKGROUND

The human eye functions to provide vision by transmitting light througha clear outer portion called the cornea, and focusing the image by wayof a crystalline lens onto a retina. The quality of the focused imagedepends on many factors including the size and shape of the eye, and thetransparency of the cornea and the lens. When age or disease causes thelens to become less transparent, vision deteriorates because of thediminished light which can be transmitted to the retina. This deficiencyin the lens of the eye is medically known as a cataract. An acceptedtreatment for this condition is surgical removal of the lens andreplacement of the lens function by an artificial intraocular lens(IOL).

In the United States, the majority of cataractous lenses are removed bya surgical technique called phacoemulsification. During this procedure,an opening is made in the anterior capsule and a thinphacoemulsification cutting tip is inserted into the diseased lens andvibrated ultrasonically. The vibrating cutting tip liquefies oremulsifies the lens so that the lens may be aspirated out of the eye.The diseased lens, once removed, is replaced by an artificial lens.

The IOL is injected into the eye through the same small incision used toremove the diseased lens. An insertion cartridge of an IOL injector isloaded with the IOL, the tip of the insertion cartridge is inserted intothe incision, and the lens is delivered into the eye.

Many IOLs manufactured today are made from a polymer with specificcharacteristics. These characteristics allow the lens to be folded, andwhen delivered into the eye, allow the lens to unfold into the propershape. Several manual injector devices are available for implantingthese lenses into the eye. However, threaded-type manual injectorsrequire the use of two hands, which is cumbersome and tedious.Syringe-type injectors produce inconsistent injection force anddisplacement. Thus, improved devices and methods are needed fordelivering IOLs into the eye.

SUMMARY

Embodiments of the present invention include various devices forimplanting an intraocular lens (IOL) into the lens capsule of an eye, aswell as methods for controlling such a device. According to an exemplaryembodiment, an IOL injection device comprises a tubular housing with aplunger longitudinally disposed within the tubular housing. The plungeris longitudinally translated frontwards and rearwards, with respect to afront end of the housing, by an electric drive system disposed withinthe housing and comprising an electric motor. The device is configuredso that when the plunger is translated towards the front of the device,its tip engages an intraocular lens insertion cartridge mounted at ornear the front end of the housing. The plunger tip, which may in someembodiments be a removable plastic sleeve that snap fits to a push rod,passes through the insertion cartridge to fold and displace anintraocular lens disposed within, and to inject the folded lens into thelens capsule of an eye.

In various embodiments, the IOL injection device further comprises acontrol circuit, electrically connected to the electric motor andconfigured to start translation of the plunger, responsive to userinput. The circuit is further configured to detect at least one faultcondition, based on a counter-electromotive force produced by theelectric motor, and to stop translation of the plunger assemblyresponsive to the detected fault condition. The detected fault conditionmay comprise excessive resistance to forward translation of the plunger,compared to a pre-determined threshold, such as might occur with animproperly loaded or otherwise occluded insertion cartridge. Someembodiments might be configured to detect excessive resistance torearward translation of the plunger, compared to a second pre-determinedthreshold, and/or insufficient resistance to forward translation of theplunger, compared to a third pre-determined threshold.

In some embodiments, the control circuit is configured to monitor therotational speed of the electric motor, based on thecounter-electromotive force, and to detect at least one fault conditionby comparing the monitored rotational speed to a pre-determinedthreshold. In some embodiments, the control circuit is configured totrack the longitudinal position of the plunger, based on thecounter-electromotive force produced by the electric motor, and todetect the at least one fault condition based on the trackedlongitudinal position. In some of these embodiments, the control circuitis configured to detect the at least one fault condition based oncomparing the counter-electromotive force produced by the electric motorto a threshold that varies with the tracked longitudinal position, suchas by comparing the monitored rotational speed to a threshold thatvaries with the tracked longitudinal position.

In an exemplary method for controlling a device for implanting anintraocular lens in the lens capsule of an eye, wherein the devicecomprises a plunger longitudinally disposed inside a tubular housing andan electric drive system including an electric motor and configured tocause longitudinal translation of the plunger along a primary axis ofthe housing, longitudinal translation of the plunger is initiatedresponsive to user input. The translation of the plunger is stoppedresponsive to detection of at least one fault condition based on acounter-electromotive force produced by the electric motor. Detectedfault conditions may include one or more of: excessive resistance toforward translation of the plunger, compared to a first pre-determinedthreshold; excessive resistance to rearward translation of the plunger,compared to a second pre-determined threshold; and insufficientresistance to forward translation of the plunger, compared to a thirdpre-determined threshold.

In some embodiments, the method may include monitoring the rotationalspeed of the electric motor, based on the counter-electromotive force,so that the fault condition is detected by comparing the monitoredrotational speed to a pre-determined threshold. In some embodiments, thelongitudinal position of the plunger is tracked, based on thecounter-electromotive force, and the detection of the fault condition isbased on the tracked longitudinal position. The fault condition may bedetected in some embodiments by comparing the counter-electromotiveforce produced by the electric motor to a threshold that varies with thetracked longitudinal position, for instance by comparing a monitoredrotational speed to a threshold that varies with the trackedlongitudinal position.

Of course, those skilled in the art will appreciate that the presentinvention is not limited to the above features, advantages, contexts orexamples, and will recognize additional features and advantages uponreading the following detailed description and upon viewing theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of an exemplary IOL injection apparatus,with an insertion cartridge installed.

FIG. 2 is a partly cut-away isometric view of the actuating mechanism ofan exemplary IOL injection device.

FIG. 3 illustrates the electric drive system and coupling mechanism ofan exemplary IOL injection device.

FIG. 4 illustrates a removable plunger tip according to some embodimentsof the present invention.

FIG. 5 is a cross-sectional view of an IOL injection device according tosome embodiments of the present invention.

FIG. 6 illustrates a fully retracted actuating apparatus.

FIG. 7 illustrates a partially extended actuating apparatus.

FIGS. 8A and 8B are cross-sectional views of alternative embodiments ofthe device of FIGS. 6 and 7, taken along line VIII.

FIG. 9 is another cross sectional view of FIGS. 6 and 7, taken alongline IX.

FIG. 10 illustrates a plunger tip wrench according to some embodimentsof the invention.

FIG. 11 illustrates the plunger tip wrench of FIG. 10 installed on anexemplary IOL injection device.

FIG. 12 is a schematic diagram illustrating an exemplary control circuitfor an IOL injection device.

FIG. 13 is a process flow diagram illustrating a method for controllingan IOL injection device according to some embodiments of the presentinvention.

FIGS. 14A and 14B illustrate an exemplary detention feature for use witha disposable plunger tip.

DETAILED DESCRIPTION

FIG. 1 illustrates a handheld intraocular lens (IOL) injection device 10for implanting an IOL into the anterior capsule of the eye. As pictured,IOL injection device 10 includes a cable assembly 12 that carries powerand/or control signals from a separate user console (not shown),although some embodiments may include one or more batteries in the mainhousing 15 to provide electrical power to the device and/or one or moreswitches or other user input devices to control the operation of thedevice. The pictured IOL injection device 10 also comprises a cartridgemount 18, which holds a removably mounted insertion cartridge 20. Aswill be explained in further detail below, the insertion cartridge 20 insome embodiments is a disposable polymeric component adapted toaccommodate an unfolded IOL lens and to fold and displace the lens as aplunger tip 25 is translated forward from the body of the housing 15 andthrough the insertion cartridge 20. In some embodiments, the cartridgemount 18 may comprise a metallic “nosecone” that includes a uniquecutout to accommodate the IOL cartridge and that is press-fitted to aninner shell of the housing 15.

FIG. 2 illustrates a partially cut-away view of an exemplary embodimentof IOL injection device 10, showing the internal workings of anactuating assembly 30 for linearly translating the plunger tip 25 alongthe primary axis of the device's housing. FIGS. 3 and 4 provide detailsof the assembly of FIG. 2, and FIG. 5 illustrates a cross-sectional viewof the IOL injection device 10.

In the pictured embodiment, the actuating assembly comprises, inaddition to the plunger tip 25, a plunger 32 configured for longitudinaltranslation inside an internally threaded tubular coupler 35 and anelectric drive system 38. As shown in FIGS. 3 and 5, the electric drivesystem 38 may comprise an electric motor 42 and gear set 44 disposedwithin a weldment and configured to rotate the tubular coupler 35, whichis held in place by a polymeric coupler sleeve 48. The internal threadson the tubular coupler 35 engage an externally threaded male coupler 46at the rear end of the plunger 32, forcing linear translation of theplunger 32 and plunger tip 25 within the tubular coupler 35, in responseto activation of the drive system 38. The internal threads of thetubular coupler 35 and/or the threads of the male coupler 46 are coatedwith a lubricant (which may be a dry film coating such as Endura 200TX,Brycoat WS2, Teflon/FEP, or the like) to minimize friction. O-rings 39,which may be formed from an elastomer, provide a seal to the tubularhousing 15, preventing moisture and/or other contaminants from reachingthe interior of the housing 15.

In some embodiments, the electric drive system 38 comprises a brushlessDC motor 42 for providing rotational torque to the gear set 44, which inturn rotates the tubular coupler 35 to extend or retract the plunger 32.The gear set 44 is effective to reduce the angular velocity of the motoraccording to a pre-determined reduction ratio, e.g., 125:1. Thisincreases the available torque from the drive system 38, and slows thelinear motion of the plunger 32 to a speed appropriate for the IOLinjection procedure.

In some embodiments, plunger tip 25 may be removable from the plunger32, as shown in FIG. 4. In these embodiments, plunger tip 25 maycomprise a disposable plastic sleeve that attaches to the forward end ofthe plunger 32, in some cases according to a “snap-fit” mechanism. Theend of the plastic sleeve that engages the IOL is more compliant than abare metallic plunger would be, and has a smooth surface finish, thusavoiding damage to the IOL as it is pushed through the insertioncartridge 20 and into the eye. The use of a disposable plastic sleevemay also ease re-processing of the IOL injection device 10 between uses.

FIGS. 6, 7, 8, and 9 provide additional details for an exemplary IOLinjection device according to some embodiments of the present invention.FIGS. 6 and 7 illustrate a longitudinal cross-section of IOL injectiondevice 10 with the plunger 32 in fully retracted and in partiallyextended positions, respectively. In the partially extended positionillustrated in FIG. 7, the plunger tip 25 is just beginning to pass intothe insertion cartridge 20.

As seen in FIG. 6, the male coupler 46, which is bored and “keyed” alongits axis to accommodate the plunger 32, is held in place with aretaining ring 52 that clips into a circumferential groove at the rearend of the plunger 32, thus securing the male coupler 46 in place. Atthe opposite end of the tubular coupler 35, a bearing assembly 54, heldin place by a polymeric bearing sleeve 56, holds the tubular coupler 35in a position concentric to the housing and facilitates smoothrotational motion of the tubular coupler 35. A compression seal 58,comprising an elastomer jacket and a metal channel ring, provides a sealto prevent moisture ingress. The plunger 32, which has a cross sectionwith two flat faces, is prevented from rotating relative to the housingby an orientation insert 60, which is held in place by pins 62.

FIGS. 8A and 8B provide cross-sectional views, corresponding to thesection indicated as “VIII” in FIG. 7, of two different embodiments ofIOL injection device 10. As seen in each of these figures, a drive shaft82 extending from the gearbox 44 engages a keyed endplate 84 of tubularcoupler 35 to transfer rotational torque of the drive system 38 to thetubular coupler 35. Tubular coupler 35 is surrounded by coupler sleeve48 and an inner shell 86 and outer shell 88 of the housing 15. In theembodiment pictured in FIG. 8B, the endplate 84 of tubular coupler 35 isslotted to subtend an arc that exceeds the portion of the slot occupiedby the drive shaft 82. This allows the drive shaft to rotate freely forpart of a rotation upon a reversal in direction. This feature mayfacilitate start-up of the electric motor in some embodiments, and mayalso be used in some embodiments to calibrate a monitoring circuit for a“no load” condition. As will be explained in further detail below, thiscalibration may be used to establish one or more thresholds for use infault detection.

FIG. 9 provides a cross-sectional view of some embodiments of IOLinjection device 10, corresponding to the section indicated as “IX” inFIG. 7. As noted above, plunger 32 has a non-circular cross section, andis held in place by orientation insert 60, which is in turn secured intoposition within the inner shell 86 and outer shell 88 of the housing byretaining pins 62. Because the plunger 32 is thus prevented fromrotating, relative to the housing, rotation of tubular coupler 35 by theelectric drive system 38 is converted into translational displacement ofplunger 32 along the axis of the IOL injector device, as shown in FIGS.6 and 7.

As shown above, in some embodiments of an IOL injector device a plungerassembly comprises two or more parts, including a push-rod 32 and aplunger tip 25. In some embodiments, plunger tip 25 may comprise aremovable plastic sleeve that snap-fits onto the plunger 32, and may bedisposable after use. In some embodiments, a plunger tip wrench may beused to install the plastic plunger tip 25 onto the plunger 32. FIG. 10illustrates an exemplary plunger tip wrench 90 with a plunger tip 25held inside. FIG. 11 shows the plunger tip wrench 90 installed onto thecartridge mount 18.

In the pictured embodiment, the plunger tip wrench 90 is secured ontothe cartridge mount 18 in the same manner as the insertion cartridge 20.In some embodiments, the plunger tip 25 is automatically installed ontothe plunger 32 in response to user activation of an installation mode.For example, after the user pushes an appropriate button on device or onan accompanying operator console, the plunger 32 is actuated at adefault speed to snap fit the plunger into the disposable sleeve. Thisactuation is followed by retraction of the plunger 32 to its originalstarting position at a default speed. The retraction pulls the plungertip 25 from the plunger tip wrench 90, which may then be removed andreplaced with a loaded IOL insertion cartridge 20. As will be discussedin further detail below, both operations may automatically terminatedresponsive to monitoring of the counter-electromotive force (oftencalled “back EMF”) produced by the spinning electric motor 42.

In some embodiments in which a disposable plunger tip 25 is used, theplunger tip 25 and the insertion cartridge 20 may be provided withfeatures so that the plunger tip 25 is automatically removed from theplunger 32 after use. In some of these embodiments, for example, theplunger tip 25 may be provided with one or more “teeth,” or otherprotrusions, designed to engage with a corresponding catch on theinsertion cartridge 20 when the end of the plunger tip 25 passes fullythrough the insertion cartridge 20. Once engaged, such a detentionmechanism provides enough resistance to backwards movement of theplunger tip 25 so that the disposable sleeve ejects itself from theplunger. When the plunger 32 is fully retracted, the insertion cartridge20 and the plunger tip 25 can be removed from the IOL injector as aunit, and discarded.

FIG. 14 illustrates an exemplary detention mechanism, as discussedabove. FIG. 14A provides a top view of plunger tip 25 fully insertedinto insertion cartridge 20, while FIG. 14B illustrates an exemplarydetention mechanism 140, comprising mating detention features on theplunger tip 25 and insertion cartridge. In the exemplary embodiment ofFIG. 14B, a protrusion from plunger tip 25 engages a lower lip of theinsertion cartridge 20 when the plunger tip 25 is in its fully extendedposition.

FIG. 12 illustrates an exemplary control circuit 100, according to someembodiments of the invention, for controlling the operation of an IOLinjection device. The pictured control circuit 100 is for a three-phase,brushless DC motor 42 that includes Hall-effect sensors 104. Althoughnot shown in FIG. 12, the motor 42 may in some embodiments provide aneutral reference point; those skilled in the art will appreciate thatthe presence of a neutral terminal simplifies the measurement of backEMF, but is not absolutely necessary. In any case, those skilled in theart will appreciate that the circuit of FIG. 12 may be readily adaptedfor motors of different types, including brushed motors. In particular,those skilled in the art will appreciate that techniques for controllinga brushless DC motor without the use of Hall-effect sensor feedback arewell known.

The control circuit 100 includes a control processor 95 which producespulse-width modulated (PWM) control signals for commutating the motor42, as well a driver circuit 98 for converting the digital controlsignals into analog drive signals applied to the stator winding inputsA, B, and C. Control circuit 100 further includes a sampling circuit 97for detecting back EMF signals from the motor's rotor inputs A, B, andC; in some embodiments, sampling circuit 97 includes analog-to-digitalconverters to convert the voltages at the motor inputs to digitalsignals for use by control processor 95. In some embodiments, samplingcircuit 97 may be synchronized to the PWM control signals produced bycontrol processor 95, so that the back EMF for a given rotor input isonly sampled when the drive for that input is floating. However, thoseskilled in the art will appreciate that in other embodiments the motorinputs may be sampled over the entire duty cycle, and the back EMFsignals isolated by digital processes in control processor 95. Thoseskilled in the art will appreciate that sampling circuit 97 may alsoinclude low-pass filters for each motor input signal in someembodiments, although it will be understood that the delay caused bysuch low-pass filters should be considered when the motor is operatingat a high speed.

In the pictured embodiment, control processor 95 has access to signalsfrom Hall-effect sensors 104; these sensor outputs provide an indicationof the motor's rotor position, and may be used by control processor 95to control the timing of the PWM signals according to conventionaltechniques. Alternatively, zero-crossings of the back EMF signals may bedetected, with the zero-crossing times used to synchronize the PWMsignals controlling the current applied to the motor. Again, techniquesfor starting-up and controlling a sensorless brushless motor using backEMF signals are well known. Several such techniques are described, forexample, in a master's thesis entitled “Direct Back EMF Detection Methodfor Sensorless Brushless DC (BLDC) Motor Drives,” by Jianwen Shao, Va.Polytechnic Institute and State University, Blacksburg, Va., September,2003 (available athttp://scholar.lib.vt.edu/theses/available/etd-09152003-171904/unrestricted/T.pdf).

In some embodiments of the invention, the back EMF may also be monitoredand used to detect faults in operation of the IOL injection device. Forinstance, due to the geometry of the intraocular lens and the volume ofviscoelastic injected into the insertion cartridge, a properly loadedcartridge has a unique inherent viscous resistance to the plunger, andthus provides a known load on the motor. When compared to a loadedcartridge, the empty cartridge also has a distinct load signature.Because of the relationship between torque and speed in a DC motor, anincrease in the load is reflected in a decrease in motor speed, for agiven drive level. Conversely, a decrease in the load is reflected in anincrease in motor speed. Because the back EMF of the motor is directlyproportional to the motor's rotational speed, the level of the back EMFcan be monitored to determine the motor's speed, and hence the appliedload. By comparing the monitored back EMF level at a given instance to apredetermined threshold, the control processor 95 can detect whether ornot the motor is operating at an expected speed. Thus, the controlprocessor can detect faults in operation and automatically respond(e.g., by shutting down) and/or providing feedback to the user.

For example, a load cartridge containing less than the requiredviscoelastic in the cartridge will result in a back EMF higher than anexpected level, in which case the control processor 95 can notify theuser. Conversely, when the back EMF value is less than an expectedlevel, it suggests an occluded cartridge. Again, the operation of thedevice can be shut down, and appropriate notice provided to the user. Ofcourse, “normal” operation will fall within a range of back EMF levels.Thus, two separate thresholds may be used to detect excessive resistanceto forward translation of the plunger and to detect insufficientresistance to translation of the plunger. (Distinct thresholds may applyto reverse translation of the plunger, in some embodiments.) Thedifference between these two thresholds defines the range of normaloperation.

As discussed above, the magnitude of the back EMF level is directlyproportional to the speed of the motor, and may be used to directlymonitor the speed of the motor, and thus indirectly to monitor the load,i.e., the resistance to translation of the plunger. Alternatively, thespeed of the motor may be monitored, using the back EMF, by countingzero crossings of the back EMF in a given time interval. This approacheffectively counts rotations of the motor; because of the fixedrelationship (defined by the gear box and the threads of the couplingmechanisms) between the motor and the linear translation, the number ofmotor rotations in a given time interval is directly proportional to thespeed. This estimated speed may be compared, in the same manner asdiscussed above, to pre-determined thresholds to detect faults inoperation.

In some embodiments of the present invention, counting positive-goingand negative-going zero-crossing points of the back EMF provides anadditional advantage, in that the longitudinal position of the plungercan be tracked at all times. Because the total number of net accumulatedzero-crossing points is directly proportional to the linear translationof the plunger, the longitudinal position of the plunger within thedevice may be determined at any time, given only a calibrated referencepoint. This calibrated reference point may be defined at the time ofmanufacture, in some embodiments, or at the time of use in others. Forexample, a user may be instructed to fully retract the plunger and tothen push a calibration button, setting a “zero” position for theplunger. Alternatively, a “hard stop” after retraction of the plungercan be automatically detected, using either of the methods discussedabove, thus indicating the “zero” position of the plunger.

In those embodiments of the present invention that monitor thelongitudinal position of the plunger, the tracked position informationmay be used along with the back EMF level at a given time to detect oneor more fault conditions. For instance, the plunger will be engaged withthe insertion cartridge only over a specific range of known lateralpositions. Otherwise, e.g., as the tip of the plunger is approaching thecartridge, the plunger is expected to move with little resistance. Thethreshold or thresholds used to detect a fault may vary, depending onthe lateral position of the plunger, to provide more accurate and/ormore informative fault detection. For example, the threshold fordetecting insufficient resistance to motion of the plunger may be set toa level corresponding to zero resistance for a range of lateralpositions over which free movement of the plunger is expected. Over thatsame range, the threshold for detecting excessive resistance may be setto a level corresponding to a resistance level somewhat lower than isexpected when the plunger begins to engage the insertion cartridge. Forlateral positions in which the plunger is fully engaged with thecartridge, both thresholds may be adjusted to correspond to higherresistance levels.

Similarly, the threshold levels may vary with the direction of theplunger movement, and/or between two or more modes of operation. Forexample, a separate operational mode may be defined for installation ofa removable plunger tip, in some embodiments, as was described above. Inthis installation mode, the fault detection thresholds may be quitedifferent than for the normal operating mode, to account for theexpected resistance when the push rod of the plunger assembly engagesthe plunger tip and the expected backwards resistance when the plungertip is extracted from the plunger tip wrench.

In some embodiments of the present invention, one or more of theabove-discussed thresholds is pre-determined, e.g., by factorycalibration, and stored in memory in or accessible to control processor95. (Those skilled in the art will appreciate that this memory maycomprise program memory or a separate memory storing factory-determinedparameters or the like, and may comprise any of several conventionalmemory types, including ROM, PROM, EEPROM, flash, etc.) In someembodiments, the thresholds used during operation may be adjustedrelative to a “no-load” back EMF level or corresponding “no-load”rotational speed determined upon starting up the motor. As was brieflydiscussed, this may be facilitated by designing the drive system of theIOL injector so that it has a short interval upon each reversal indirection during which the drive system is not engaged with the plunger.One design approach is shown in FIG. 8B, and was discussed above. Insuch embodiments, the “no-load” level for back EMF or speed may bemeasured and used to establish a baseline level. This baseline level maybe used to scale and/or translate stored threshold levels to obtain moreaccurate operational thresholds.

With the preceding discussions in mind, those skilled in the art willappreciate that the process flow diagram of FIG. 13 illustrates anexemplary embodiments of a method for controlling an intraocular lensinjection device according to any of the mechanical configurationsdiscussed above and variations thereof. Those skilled in the art willappreciate that this particular process flow is not intending to belimiting; numerous variations of this method falling within the scope ofthe present invention will be apparent in view of the precedingdiscussion. Those skilled in the art will further appreciate that theprocessing flow of FIG. 13 may be implemented in software or firmwarestored in program memory within or associated with control processor 95,for example, which memory may comprise one or more of variousconventional types including read-only memory (ROM), programmableread-only memory (PROM), flash memory, magnetic or optical memorydevices, or the like.

In any case, the process flow illustrated in FIG. 13 begins with IOLinjection device in an inactive state. The device checks for user inputindicating that actuation of the plunger assembly should begin, as shownat block 210. This user input may originate at any of a number ofconventional user input devices, such as a keypad or touchscreen at anoperator console connected by cable to the IOL injection device, afoot-operated switch electrically connected to the IOL injection deviceby cable or via a console, or one or more switches or buttons on thebody of the IOL injection device itself. In any case, in response touser input indicating that the plunger assembly should be moved, acontrol circuit begins translation of the plunger in the indicateddirection, as shown at block 220.

As the plunger is moved, the back EMF from the electric motor ismonitored, as shown at block 230, according to any of the techniquesdiscussed above. In some embodiments, the magnitude of the back EMFlevel is monitored and compared to one or more pre-determinedthresholds. In other embodiments, zero-crossings of the back EMF aredetected and counted for a pre-determined time interval, to get anindication of the plunger's speed, and compared to one or morepre-determined thresholds. If a fault condition is detected, asindicated at block 240, the movement of the plunger is immediatelysuspended, as shown at block 260. As discussed above, the detected faultcondition may correspond to excessive resistance to forward or backwardsmovement of the plunger, compared to pre-determined threshold levels, orinsufficient resistance to forward or backwards movement of the plunger,compared to pre-determined threshold levels. In any of these cases, thethreshold level for fault detection may vary according to a trackedlongitudinal position of the plunger, as discussed earlier. Furthermore,the operational threshold levels may be adjusted according to a baselineresistance or operating speed determined during a “no-load” condition.

In some embodiments, the stopping of the plunger's movement in responseto a detected fault may be accompanied with or followed by an alert tothe user, indicating the fault. In some cases, a message identifying aparticular type of fault (e.g., “blocked cartridge”, “empty cartridge”,or the like) may be provided to the user via a graphical user interfaceon an operator's console. If a fault condition is not detected at block240, then the status of the user input is checked, as shown at block250. If the user input indicates that movement of the plunger should bestopped, then the motor is deactivated and the plunger's translation isstopped, as shown at block 260. Otherwise, translation of the plungercontinues, as shown at block 220, and the preceding operations arerepeated until either a fault occurs or the user input indicates thatthe plunger assembly's movement should be stopped.

In the above discussion of the process flow of FIG. 13, it was assumedthat translation of the plunger continues, once initiated, until userinput directs a stop or until a fault condition is detected. Thoseskilled in the art that the plunger motion may be limited at either orboth ends by a mechanical stop. In some embodiments, these mechanicalstops may be detected by the same fault detection mechanisms asdescribed above, i.e., by monitoring the back EMF levels and/or thespeed of the motor. Alternatively, some embodiments may prevent theplunger from reaching the mechanical stops by tracking the longitudinalposition of the plunger, as described above, and automatically stoppingthe plunger's movement before it reaches a mechanical stop.

The preceding description of various embodiments of an intraocular lensinjection device and of methods for using such a device was given forpurposes of illustration and example. Those skilled in the art willappreciate, of course, that the present invention may be carried out inother ways than those specifically set forth herein without departingfrom essential characteristics of the invention. The present embodimentsare thus to be considered in all respects as illustrative and notrestrictive, and all changes coming within the meaning and equivalencyrange of the appended claims are intended to be embraced therein.

What is claimed is:
 1. A device for implanting an intraocular lens inthe lens capsule of an eye, the device comprising: a tubular housinghaving a primary axis extending between front and rear ends of thehousing; a plunger longitudinally disposed within the housing and havingfirst and second ends, the first end being disposed towards the frontend of the housing; an electric drive system disposed within thehousing, the electric drive system including an electric motor andconfigured to cause longitudinal translation of the plunger along theprimary axis of the housing; a cartridge mount at or near the front endof the housing and configured to accommodate a removable insertioncartridge in alignment with the plunger so that an intraocular lensdisposed in the insertion cartridge is displaced from the insertioncartridge as the plunger is translated towards the front end of thehousing; a control circuit, electrically connected to the electric motorand configured to start translation of the plunger responsive to userinput, to detect at least one fault condition based on acounter-electromotive force produced by the electric motor, and to stoptranslation of the plunger responsive to the detected fault condition; aremovable plunger tip configured to snap fit to the first end of theplunger so that the removable plunger tip engages the intraocular lensas the plunger is translated towards the front end of the housing; and aplunger tip wrench removably mountable to the cartridge mount andconfigured to accommodate the removable plunger tip for snap fitting tothe first end of the plunger as the plunger is translated towards thefront end of the housing and the plunger tip wrench also configured tothereafter release the removable plunger tip as the plunger istranslated towards the rear end of the housing.
 2. The device of claim1, wherein the removable plunger tip comprises a first detention featureconfigured to engage a corresponding detention feature on the insertioncartridge when the plunger tip is fully inserted into the insertioncartridge, so that the removable plunger tip is thereafter removed fromthe plunger when the plunger is translated towards the rear end of thehousing.
 3. The device of claim 1, wherein the at least one faultcondition comprises one or more fault conditions selected from the setcomprising: excessive resistance to forward translation of the plunger,compared to a first pre-determined threshold; excessive resistance torearward translation of the plunger, compared to a second pre-determinedthreshold; and insufficient resistance to forward translation of theplunger, compared to a third pre-determined threshold.
 4. The device ofclaim 1, wherein the control circuit is configured to monitor therotational speed of the electric motor, based on thecounter-electromotive force, and to detect the at least one faultcondition by comparing the monitored rotational speed to apre-determined threshold.
 5. The device of claim 1, wherein the controlcircuit is configured to detect the at least one fault condition basedon comparing the counter-electromotive force produced by the electricmotor to a threshold that varies with a longitudinal position of theplunger.
 6. The device of claim 1, wherein the control circuit isconfigured to monitor the rotational speed of the electric motor, basedon the counter-electromotive force, and to detect the at least one faultcondition by comparing the monitored rotational speed to a thresholdthat varies with a longitudinal position of the plunger.
 7. The deviceof claim 1, further comprising an insertion cartridge removablymountable to the cartridge mount and adapted to accommodate theintraocular lens and to fold and displace the intraocular lens from thedevice as the plunger is translated towards the front end of thehousing.
 8. The device of claim 1 further comprising a tubular couplercoupled to the electric drive system and rotatable by the electric drivesystem, the coupler sleeve comprising a threaded internal surfaced,wherein the second end of the plunger comprises an outer threadedsurface that matingly engages the threaded internal surface of thecoupler sleeve, and wherein the plunger is operable to longitudinallytranslate along the primary axis of the housing in response to rotationof the tubular coupler.
 9. The device of claim 1 further comprising anorientation insert and an opening formed therein, the plunger extendingthrough the opening, wherein the plunger comprises a non-circularcross-section, and wherein the opening of the orientation insert isadapted to receive the non-circular cross-section of the plunger, andwherein the plunger and the opening cooperate to permit translation ofthe plunger free from rotation of the plunger relative to the housing.10. The device of claim 1, wherein the electric drive system comprises adrive shaft comprising an end portion having semi-circularcross-section, the end portion of the drive shaft received within a slotformed within the tubular coupler, wherein the slot defines an arclength that exceeds a size of the drive shaft, such that the drive shaftis freely rotatable within the slot relative to the tubular coupler by adefined angular amount of the arc length.
 11. A device for implanting anintraocular lens in the lens capsule of an eye, the device comprising: atubular housing having a primary axis extending between front and rearends of the housing; an electric drive system disposed within thehousing, the electric drive system including an electric motor; anactuating assembly comprising: a tubular coupler coupled to the electricdrive system and rotatable by the electric drive system, the tubularcoupler comprising a threaded internal surface; and a plungerlongitudinally disposed within the housing and having a first end and asecond end, the first end being disposed towards the front end of thehousing, and the second end comprising an outer threaded surface thatmatingly engages the threaded internal surface of the tubular coupler,the plunger operable to longitudinally translate along a primary axis ofthe housing in response to rotation of the tubular coupler; a cartridgemount at or near the front end of the housing and configured toaccommodate a removable insertion cartridge in alignment with theplunger so that an intraocular lens disposed in the insertion cartridgeis displaced from the insertion cartridge as the plunger is translatedtowards the front end of the housing; and a control circuit,electrically connected to the electric motor and configured to starttranslation of the plunger responsive to user input, to detect at leastone fault condition based on a counter-electromotive force produced bythe electric motor, and to stop translation of the plunger responsive tothe detected fault condition.
 12. The device of claim 11 furthercomprising an orientation insert and an opening formed therein, theplunger extending through the opening, wherein the plunger comprises anon-circular cross-section, and wherein the opening of the orientationinsert is adapted to receive the non-circular cross-section of theplunger, and wherein the plunger and the opening cooperate to permittranslation of the plunger free from rotation of the plunger relative tothe housing.
 13. The device of claim 11, wherein the electric drivesystem comprises a drive shaft comprising an end portion havingsemi-circular cross-section, the end portion of the drive shaft receivedwithin a slot formed within the tubular coupler, wherein the slotdefines an arc length that exceeds a size of the drive shaft, such thatthe drive shaft is freely rotatable within the slot relative to thetubular coupler by a defined angular amount of the arc length.
 14. Thedevice of claim 11, wherein the at least one fault condition comprisesone or more fault conditions selected from the set comprising: excessiveresistance to forward translation of the plunger, compared to a firstpre-determined threshold; excessive resistance to rearward translationof the plunger, compared to a second pre-determined threshold; andinsufficient resistance to forward translation of the plunger, comparedto a third pre-determined threshold.
 15. The device of claim 11, whereinthe control circuit is configured to monitor the rotational speed of theelectric motor, based on the counter-electromotive force, and to detectthe at least one fault condition by comparing the monitored rotationalspeed to a pre-determined threshold.
 16. The device of claim 11, whereinthe control circuit is configured to detect the at least one faultcondition based on comparing the counter-electromotive force produced bythe electric motor to a threshold that varies with a longitudinalposition of the plunger.
 17. The device of claim 11, wherein the controlcircuit is configured to monitor the rotational speed of the electricmotor, based on the counter-electromotive force, and to detect the atleast one fault condition by comparing the monitored rotational speed toa threshold that varies with a longitudinal position of the plunger. 18.The device of claim 11, further comprising an insertion cartridgeremovably mountable to the cartridge mount and adapted to accommodatethe intraocular lens and to fold and displace the intraocular lens fromthe device as the plunger is translated towards the front end of thehousing.
 19. The device of claim 11, further comprising a removableplunger tip configured to snap fit to the first end of the plunger sothat the removable plunger tip engages the intraocular lens as theplunger is translated towards the front end of the housing.
 20. Thedevice of claim 19, further comprising a plunger tip wrench removablymountable to the cartridge mount and configured to accommodate theremovable plunger tip for snap fitting to the first end of the plungeras the plunger is translated towards the front end of the housing andthe plunger tip wrench also configured to thereafter release theremovable plunger tip as the plunger is translated towards the rear endof the housing.
 21. The device of claim 19, wherein the removableplunger tip comprises a first detention feature configured to engage acorresponding detention feature on the insertion cartridge when theplunger tip is fully inserted into the insertion cartridge, so that theremovable plunger tip is thereafter removed from the plunger when theplunger is translated towards the rear end of the housing.